
where \(0<q<1\)  and \(\epsilon \)  is a small positive number to make (REF ) differentiable. When \(q\)  and \(\epsilon \)  are close to zero, one can use \(c_a\left\Vert \mathbf {x}_{j,1}+\epsilon \mathbf {1}\right\Vert _q^q\)  to efficiently approximate (REF ) [1]}, [2]}, [3]}.
